Lagoon systems for treatment of wastewater have long been in use and have achieved considerable popularity, especially in areas where land is readily available. A lagoon system typically involves use of an earthen basin in which the wastewater is contained. The organic wastes are converted to biological solids, either by operating the system as a simple stabilization pond or by using low rate partial mix aeration. The biological solids eventually settle and are retained on the bottom of the lagoon.
Aerated lagoon systems are simple and economically advantageous because expensive equipment is not required and there is no need for highly trained personnel to operate the facility. However, substantial amounts of land are required because of the need to detain the wastewater in the lagoon for an extended period to achieve significant levels of treatment. Also, the overall capacity or treatment level is limited, as virtually no flexibility is available in the treatment process.
By way of example, a typical lagoon system may require 15 to 30 days detention time to remove most carbonaceous BOD and oxidize ammonia during warm weather. In the upper midwest and other relatively cold climates, the lagoon temperature in the winter is too cold for nitrification to be carried out. With the increased emphasis that is being placed on the nitrification of ammonia, and with regulatory requirements being gradually expanded to require nitrification for all systems, the basic lagoon technology is severely handicapped due to its inability to consistently nitrify ammonia, particularly in cold climates. Many small municipalities have significant investment in an existing lagoon system and lack the financial capability to construct more advanced treatment facilities such as an activated sludge plant that is capable of meeting the regulatory requirements for nitrification and/or denitrification. Further, the costs of training operating personnel and maintaining more sophisticated systems are often beyond the capability of rural water districts and small municipalities.